Field of the Invention
The present invention relates to a content output device and a program, and in particular, can be suitably utilized for a content output device in which a plurality of programs including the program perform multimedia processing by operating on a processor.
Description of the Related Art
In multimedia processing, in order to increase a parallel degree of processing, various types of application programs are divided into a plurality of threads, respectively, and a series of threads that executes the same application is coupled to each other via a buffer. The buffer holds (also called “buffers” or “accumulates”) data output from one thread until the data is used by other threads. A data amount held in the buffer increases and decreases according to a difference between a speed at which data is output from a previous thread and a speed at which a subsequent thread uses the data. When the threads originating from a plurality of applications are executed in parallel, the subsequent thread that uses data held in the buffer is often kept waiting due to processing of other threads in parallel, and an increase and decrease width of the data amount held in the buffer becomes large. In the multimedia processing, control using threads is performed as described above. In addition, in a system that has employed an OS (Operating System), such as Linux (a registered trademark, and the same hereinafter), multimedia processing may be performed in parallel without previously deciding priority of threads. There is a case of giving such system a function to receive and reproduce digital television broadcasting. For that purpose, since start of each thread may be delayed, and thus sound interruption and non-smoothness of video may possibly occur, it is necessary to enlarge a buffer between the threads. However, enlarging the buffer causes deterioration of responsiveness to user operation.
Japanese Patent Laid-Open No. 2011-35775 (Patent Literature 1) discloses a moving image output device that can output video and audio without feeling of unnaturalness in response to operation of requesting viewing of moving images. Before normal reproduction that is started after buffer amounts of video data and audio data reach predetermined values, respectively, video data is output using accumulating video data at a speed lower than a reproduction speed at the time of still image output or the normal reproduction, and the audio data is output at a reproduction speed not less than a predetermined value asynchronously with the reproduction of the video data.
Japanese Patent Laid-Open No. 2001-292381 (Patent Literature 2) discloses a technology to perform slow reproduction during the period of time until channel switching processing is stabilized at the time of channel change of digital television broadcasting.
As a result of the present inventor examining Patent Literature 1 and Patent Literature 2, it turned out that there were the following new problems.
According to a technology described in Patent Literature 1, a problem in which output start of video and audio is delayed is solved even when the buffer between the threads is enlarged. However, since video is output at the low speed, and audio is output at the speed not less than the predetermined speed asynchronously with the video, synchronization of the video and the audio cannot be obtained. When a system scale becomes large, and a buffering amount needs to be increased, there occurs a problem in which, at the time of output start in a case or the like of starting output of moving images in response to operation of requesting viewing of the moving images, a period when video and audio are asynchronously output is further extended, and a period of deteriorating user visibility becomes long.
Although Patent Literature 2 describes that an audio signal that does not synchronize with video is made to be mute (a silent state), or the audio signal is decoded at a low decoding processing speed similar to a video signal, it does not disclose a specific method for that. Furthermore, it is pointed out that Patent Literature 1 “has a problem in which when an audio signal is decoded at a low decoding processing speed similar to a video signal, output audio is drawled, and a content also becomes difficult to hear”.
Although means for solving such problems is explained below, the other problems and the new feature will become clear from the description of the present specification and the accompanying drawings.